The present invention relates to a constant speed universal joint comprising inner and outer complementary body members, rolling elements between the body members adapted for transmitting torque from one member to the other.
Constant speed joints of the above type are not new per se as illustrated for example in U.S. Pat. No. 1,975,758. In the embodiment illustrated in FIGS. 8 and 9 of this prior patent, a control disk is provided having axial retaining fingers incorporated between the inner and outer joint body members which serves to guide the spherical rolling elements on one longitudinal side and maintains them in a plane bisecting the angle between the axes of rotation of the two joint body members. This prior known constant speed joint has several disadvantages and drawbacks. For example, since the rolling elements are slidably guided on only one longitudinal side in the bisecting plane, a sliding guide is therefore lacking on the other side of the two longitudinal sides and as a consequence the rolling elements are not always maintained precisely in the bisecting plane and controlled. Accordingly, as a result of this lack of guidance under certain operating conditions, the rolling elements produce additional parasitic forces between the inner and outer joint body members which are not desirable. A further disadvantage resides in the fact that the retaining disk between the inner and outer joint body members must be assembled in such a way that it restricts the space for the rolling elements and thus the ability within a given sized joint to use the large maximum load bearing rolling elements is sacrificed. Additionally, the retaining fingers which engage axially in the inner and outer grooves of the inner and outer joint body members are subjected to bending stresses and it has been observed that they tend to break off during extreme operations under high loads.
In accordance with the embodiment shown in FIGS. 1 and 2 of prior U.S. Pat. No. 1,975,758, a cage instead of a retaining disk is inserted between the inner and outer body members to maintain the rolling elements in the bisecting plane. This cage occupies a relatively large space measured in a radial direction between the joint body members. Consequently, it is necessary to insert relatively large rolling elements between the inner and outer joint body members so that they protrude from the pockets of the cage and can engage in the inner and outer grooves of the joint body respectively for torque transmission. Thus, this modified constant speed joint is of relatively large construction and is for the most part capable of only assuming relatively low torque loads.
With the foregoing in mind, it is an object of the present invention to provide a constant speed joint characterized by novel features of construction and arrangement which overcomes the drawbacks of the prior art noted above. To this end, the inner body member has a centric cavity and each inner groove penetrates the cavity in the form of a radial slit and wherein the control means are provided in the form of a member mounted in the cavity having control arms engaging radially from inside to outside through an inner groove maintaining the mating rolling elements of the inner groove in the bisecting plane. By this construction, the joint assembly is of a very compact construction which is capable of accommodating high torque loads without damage and which additionally ensures trouble-free guidance of the rolling elements in the plane bisecting the angle between the axes of rotation.
In the preferred embodiment of the invention, the control arms of the control member are constructed as pins lying in the bisecting plane and the rolling elements have radial bores therein to receive the pins providing for free rotating support of the rolling elements. This arrangement provides an extremely compact construction wherein the control means do not occupy any space at all at the longitudinal side of the rolling elements. By reason of this, the rolling elements can roll in the inner and outer grooves without lateral restriction by the control means when the axes of rotation of the two joint body members are mutually displaced. In this manner, a greater bending angle of the axis of rotation in the inner joint body member in relation to the axis of rotation of the outer joint body member can be permitted in the constant speed universal joint.
The control arms are preferably provided on both longitudinal sides of the mating rolling element with a retaining finger slidably supporting the rolling elements. By this arrangement, the rolling elements are held at both longitudinal ends by the retaining fingers of the control arm and guided in the bisecting plane.
In accordance with another feature of the present invention, a spherical cup having a convex curved outer surface which is ductile under elastic pressure in a longitudinal direction is positioned opposite and closely fitted to one of the support surfaces of the cavity in the control body. In this manner, the control body can perform rotating and swivelling movements as well as shift itself slightly as the result of pressure in the longitudinal direction against the elastic ductile outer surface. This, facilitates assembly of the control body and the rolling elements in the inner and outer universal joint body members. Furthermore, by this arrangement, it is possible during operation for the control body to make small relative adjusting movements in the constant speed universal joint so that jamming of the control body between the two joint body members is obviated.
In accordance with still another more specific feature of the invention, the inner and outer joint body members are provided with four complementary grooves wherein the center of curvature of one pair of diametrically opposed outer grooves is arranged on one side and the center of curvature of the mating pair of inner grooves is arranged on the other side of the bisecting plane and the center of curvature of the other pair of diametrically opposed grooves in relation to the center of curvature of its mating pair of inner grooves is arranged at opposite sides of the bisecting plane. By this arrangement, the longitudinal thrust of one pair of diametrically opposed rolling elements produced by a torque load is at least partly compensated by the longitudinal thrust of the other pair of diametrically opposed rolling elements of the universal joint which acts in the opposite direction. In this manner, relatively low longitudinal forces, that is, thrust forces in the direction of the axes of rotation, are formed at the joint rolling elements so that an extremely quiet, vibration-free running of the constant speed universal joint with low running friction of the rolling elements is obtained. There is another advantage to this arrangement in that the joint in the assembled relation is self-retaining. For example, the inner joint body member is fixed against slipping out to the other side in the outer joint body member by the two diametrically opposed rolling elements of the two outer grooves, the center of curvature which lies on the one side of the bisecting plane. Similarly, the inner joint body member is held in place longitudinally in the outer joint body member by the rolling elements in the two other diametrically opposed outer grooves which have their center of curvature on the other side of the bisecting plane.
A further specific characteristic of the present invention resides in the bisecting plane being arranged to bisect the connecting line through the two centers of curvature of the inner and outer grooves in the center between these two centers of curvature thus providing a simple side-to-side symmetrical construction of the inner and outer grooves in the inner or outer joint bodies respectively. This arrangement coupled with the spherical cup having a convex ductile outer surface results in balancing of the longitudinal forces produced by the rolling elements in the inner and outer grooves so that they compensate each other completely. Furthermore, because of this a relatively low longitudinal thrust is exerted on the two joint body members by the rolling elements during a torque load so that the two joint body members can be held in place securely by relatively simple means on their driving elements or machine shaft.
In accordance with another specific feature of the constant speed universal joint, the outer joint body member is formed with a spherical concave inner surface and the inner joint body has a spherical convex outer surface which is slidably and angularly movable in the inner joint body member whereby the two complementary spherical surfaces have a common sphere center which coincides with a point of intersection of the connecting line through the two centers of curvature of the inner and outer grooves with the bisecting plane. By this arrangement the inner joint body member is slidably guided centrically and angularly movable with its spherical convex outer surface on the spherical convex inner surface of the outer joint body. Thus the outer surface may be constructed in such a way that the mating inner surface is grasped and the inner joint body member is held in place in the outer joint body member on both longitudinal sides. In this case, therefore, centering forces as well as longitudinal forces of the rolling elements are not only transmitted via the inner and outer grooves of the joint bodies but also via the inner and outer surface of the inner and outer joint bodies respectively. In particular cases, the rolling elements can be completely relieved of the radially directed centering forces between the inner and outer joint bodies and the rolling elements then only take up the forces between the inner and outer joint bodies acting in a peripheral direction and caused by the torque.
In order to simplify machining and assembling of the joint, the surface of the rolling elements engaging in the inner grooves of the inner joint body and in the outer grooves of the outer joint body are of a spherical configuration and the grooves closely fit or complement the cross sectional shape of the rolling elements.